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Mathematics 19 Online
OpenStudy (anonymous):

limit

OpenStudy (anonymous):

\[\lim_{x \rightarrow 1}\frac{ \sqrt[3]{x}-1 }{ \sqrt[4]{x}-1 }\]

OpenStudy (nubeer):

familiar with L'hopital rule?

OpenStudy (anonymous):

no

OpenStudy (anonymous):

I tried substitution but it does not work

OpenStudy (anonymous):

is there any way you can do it without the rule

hartnn (hartnn):

yes

OpenStudy (nubeer):

hmm yes.. what is the highest possible power of x that can be in your question?

hartnn (hartnn):

so mulriply and divide by x-1 a=1

hartnn (hartnn):

\(\huge\lim_{x \rightarrow a}\frac{ {x^n}-a^n}{ x-a }=na^{n-1}\)

hartnn (hartnn):

n=1/3 in numerator and 1/4 in denom.

OpenStudy (anonymous):

could we first try with \[t^3=\sqrt[3]{x}\]

hartnn (hartnn):

not required, i think...

OpenStudy (anonymous):

\[\frac{ (x^{1/3}-1)(x-1) }{ (x^{1/4} -1)(x-1)}\]

hartnn (hartnn):

more like \(\huge \frac{\frac{x^{1/3-1}}{x-1}}{\frac{x^{1/4}-1}{x-1}}\)

hartnn (hartnn):

don't multiply them out, bring it in the form as i shown

hartnn (hartnn):

then just use formula in num and denom

OpenStudy (anonymous):

okay

OpenStudy (anonymous):

\[\frac{ (x^{1/9}-1)(x^{2/9}+x^{1/9}+1) }{ (x^{1/8}-1)(x^{1/8}+1) }\] I think

hartnn (hartnn):

what the ... ?

OpenStudy (anonymous):

ohhh sorry I am supposed to use the rule above not factorise

hartnn (hartnn):

plz go through my comments....

OpenStudy (anonymous):

\[\frac{ 1/3x^{-2/3} }{ 1/4x^{-3/4} }\] then limit becomes\[\frac{ 1/3 }{ 1/4 }=4/3\]

hartnn (hartnn):

thats good now :)

hartnn (hartnn):

doubts ?

OpenStudy (anonymous):

the formular you used looks like the derivaetive rule

hartnn (hartnn):

according to formula its \(\huge \frac{ 1/3 (1)^{-2/3} }{ 1/4(1)^{-3/4} }\)

OpenStudy (anonymous):

or binomial

hartnn (hartnn):

it is.....i don't know whether u can use it directly here....

OpenStudy (anonymous):

thanks now I get it so does not depend on the value we are approaching

hartnn (hartnn):

it does, \(\huge\lim_{x \rightarrow a}\frac{ {x^n}-a^n}{ x-a }=na^{n-1}\) the limit depends on a

hartnn (hartnn):

here fortumately a=1

OpenStudy (anonymous):

yes it is really helpful I will call it L'Hartnn rule

OpenStudy (anonymous):

thanks

hartnn (hartnn):

lol! :P welcome ^_^

OpenStudy (anonymous):

if we let \[x=t^{12}\]\[\frac{ t^4-1 }{ t^3-1 }=\frac{ (t-1)(t+1)(t^2+1) }{ (t-1)(t^2+t+1) }=\frac{ (t+1)(t^2+1) }{ t^2+t+1 }\] \[\frac{ 2(2) }{ 1+1+1 }=4/3\]

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